Due to the historical reason, the type boundary feature is delivered
from hierarchical types in libsepol, it has supported boundary features
both of subject type (domain; in most cases) and target type.

However, we don't have any actual use cases in bounded target types,
and it tended to make conceptual confusion.
So, this patch removes the dead code to apply boundary checks on the
target types in libsepol (when expand-check=1). I makes clear the TYPEBOUNDS
restricts privileges of a certain domain bounded to any other domain.